The invention relates generally to color copying.
More particularly, the invention relates to a method of copying color exposures which may have been made with light of different color temperature, e.g. color exposures which may have been made using either artificial light or sunlight.
When copying color exposures in accordance with the neutral gray compensation principle, color correction factors are employed in order to produce copies which, overall, have an essentially neutral gray color composition. Since the values of the correction factors depend upon the type of light used to illuminate the exposures, it is necessary to determine how the latter were exposed.
The West German Offenlegungsschift No. 27 22 321=U.S. Pat. No. 4,192,605 discloses a copying method in which the type of light is established by measuring the density of a color exposure in each of the three primary colors. The difference between the densities of two colors affected by the type of illumination is calculated, and this difference compared with a reference value to thereby determine how the exposure was made.
In the preceding method, an integral or overall density is obtained for each color. In other words, only one density measurement each in red, green and blue is made on each exposure. The differences calculated from these integral densities are strongly influenced by the color distribution in the exposure. Thus, intensely yellow motifs, e.g., yellow-clad people stationed in front of a brick wall, cannot be distinguished in an exposure made with artificial light having a low color temperature.
Other color copying methods have become known in which the density in each primary color is measured at a multiplicity of regions of an exposure. The densities are evaluated statistically in order to determine the type of light used in making the exposure. These methods give rise to the same effects as for integral density measurements.